Postpartum is a specific event that often results in decreased physical activity (PA) for women;thereby placing this special population at increased risk for several chronic diseases and premature mortality. The existing research examining PA during postpartum is limited, however, with respect to the following 3 important factors: (a) cross-sectional assessments that do not capture the specific physical and psychological demands of early, middle, and late postpartum;(b) nonstandardized and unvalidated PA measures;and (c) nontheoretical studies of PA motivators and predictors. Before effective PA interventions are implemented with postpartum women, it is necessary to prospectively examine their PA beliefs and behaviors using standardized measures of PA behavior within a theoretical framework. This approach will provide the theoretical basis to implement PA interventions specific to the physical, environmental, and psychological demands of postpartum. The theory of planned behavior (TPB) is one of the most influential and successful theories for understanding and predicting PA intention and behavior, and will serve as the theoretical framework to prospectively determine the PA beliefs and behaviors for women at 6 weeks, 3 months, and 6 months postpartum. The overall objectives of our proposal are to: a) determine and examine the predictive ability of the TPB for postpartum women;b) examine PA levels during postpartum (i.e., min of moderate-strenuous PA per week, energy expenditure, mean counts/min, and days/min of PA to meet current PA guidelines);and c) evaluate theory-based demographic, quality of life, and environmental moderators of PA behaviors, as guided by the TPB. The results from this proposal will be used to design a theory-based randomized clinical trial to increase and maintain PA of postpartum women. PUBLIC HEALTH RELEVANCE: Before effective PA interventions are implemented with postpartum women, it is necessary to prospectively examine their PA beliefs and behaviors using standardized measures of PA behavior within a theoretical framework. This approach will provide the theoretical basis to implement PA interventions specific to the physical, environmental, and psychological demands of postpartum. Guided by the theory of planned behavior we will prospectively determine the PA beliefs and behaviors (i.e., accelerometers and self-report) for women at 6 weeks, 3 months, and 6 months postpartum, and variables that moderate the theory of planned behavior and PA relationship.